An electric motor lifts a load of weight $W$ through a vertical height $h$ in time $t$ - AQA - A-Level Physics - Question 27 - 2019 - Paper 1

To determine the efficiency of the electric motor, we need to calculate the useful work done and the electrical energy supplied to the motor.

1. Calculate Useful Work Done: The work done by the motor in lifting the load is given by: $ext{Work} = W imes h$

2. Calculate Electrical Energy Supplied: The electrical energy supplied to the motor can be calculated using the formula: $ext{Energy} = V imes I imes t$

3. Calculate Efficiency: The efficiency ($ext{Efficiency}$) can be calculated as follows: ext{Efficiency} = rac{ ext{Useful Work Done}}{ ext{Electrical Energy Supplied}} = rac{Wh}{VIt}

Thus, the efficiency of the motor is represented by the expression: rac{Wh}{VIt}.